I am using themattharris’ OAuth PHP library (which works perfectly by the way), but I stumbled upon a problem during the OAuth authentication.
When I try to tweet something, I get the following error message;

The “Could not authenticate with OAuth” error means the oauth_token and oauth_secret are no longer valid. Earlier today we had some similar reports saying the values copied directly from the “Your access token” section of this site were not working.

I’m using Twitterizer .NET library for posting tweets within a web-site into my twitter account. It works just fine on site, running on my local server (authenticates with OAuth through twitter app and posts a tweet). But when I’m trying to post a tweet on production server, Twitterizer says: “Result = Unauthorized. ErrorMessage = Could not authenticate with OAuth.”

I double checked consumer keys, also tried to reset the keys, create another app and try again - same result.

Twitter application has read/write access to my twitter account and is not blocked. This problem appeared suddenly on 08/12 after a period of successful working for about a month, when tweets were posted every hour or so.